1. Field of the Invention
This invention relates to bobbin assemblies for supplies of thread as used on different sewing machines and, more particularly, to a bobbin assembly having structure which cooperates with a support for the bobbin assembly to prevent backlash of thread due to overrunning.
2. Background Art
Bobbins are used for thread supplies on a wide range of sewing equipment. Typically, the bobbin has a core with a rotational axis and axially spaced flanges which bound a storage space for thread wrapped around the core. The bobbin is mounted on a support for rotation around the core axis. By rotating the bobbin, thread wrapped around the core is controllably paid out.
Ideally, the bobbin is guidingly rotated during operation without any significant resistance as might cause uneven line distribution or, in a worse case, jamming of the bobbin. While smooth rotation of the bobbin is desirable during sewing operations, the unimpeded rotation of the bobbin potentially causes thread backlash. Ideally, as the machinery is stopped, the bobbin rotation simultaneously ceases. However, due to the free rotation of the bobbin, the momentum of the rotating bobbin causes it to continue to rotate which could produce a backlash in the thread. This may require that the machinery be shut down to allow the backlash to be eliminated. Severely backlashed thread may have to be cut. Potentially, there is a significant loss of operating time, as well as the inconvenience of having to manually remedy the backlash situation. Severe backlashing may require replacement of the bobbin with a bobbin having a new supply of thread. Consequently, significant amounts of thread may be wasted.
Potentially of greater significance is the fact that a slackened thread resulting from overrunning of the bobbin may cause at least temporary defective stitching after the equipment is re-started. This may lead to defective product that may have to either be restitched or destroyed.
To address this problem, it is known to install disk-like spring elements on a case which confines the bobbin into its operative position. These springs have deflectable arms which produce a frictional bias force on the bobbin. This force is preferably controlled so that it does not significantly impede rotation of the bobbin during a sewing operation yet produces enough resistance that the bobbin will not continue to rotate once the equipment is stopped as might cause thread backlash.
In one form, the invention is directed to the combination of a bobbin assembly and a support for the bobbin assembly. The bobbin assembly has a core around which a supply of thread can be wrapped. The core has a rotational axis. The bobbin assembly further has a first flange with first and second oppositely facing surfaces. The first surface bounds a storage space for thread wrapped around the core. The first flange has at least one projection from the second surface. The support has a third surface facing the second surface and bearing against the at least one projection for limiting movement of the spool in a direction substantially parallel to the rotational axis with the bobbin assembly operatively connected to the support.
The combination may include a supply of thread wrapped around the core. In one form, the first and second surfaces have substantially the same area and the at least one projection occupies an area that is less than the area of the second surface.
The at least one projection may be formed as one piece with the first flange or separately formed and fixedly attached to the first flange.
In one form, the bobbin assembly has a second flange that is spaced along the rotational axis from the first flange so that the first and second flanges cooperatively bound the thread storage space.
In one form, there are a plurality of projections from the second surface which bear against the third surface of the bobbin assembly, with the bobbin assembly operatively connected to the support.
The at least one projection may be in the form of a ridge.
The projection may be defined by roughening the second surface.
The at least one projection may be a projecting post.
The at least one projection may be defined by an element embedded in the first flange.
The first flange and at least one projection may be made from the same material or different materials.
In one form, the at least one projection is repositionable relative to the first flange, as by bending.
The at least one projection may be made from a shape-retentive material that can be selectively formed and maintained in a plurality of different configurations.
The support may be a bobbin basket and/or a bobbin case.
The bobbin basket may include a post which projects into the core. The bobbin assembly moves around the post as the bobbin basket moves around the rotational axis.
The invention is also directed to a bobbin assembly as described above, for mounting to a support.